That lead to discussions with Kalanick, and Uber’s engineering problems proved too enticing for Singhal to remain in retirement and away from tech companies:

“In fact as I dug deeper into how Uber works, it became pretty clear that this is one of the hardest — and therefore most fun — computer science and engineering challenges in the world today. It’s hard enough to connect millions of drivers to millions of riders in real time while creating optimal routes for drivers,” Singhal said in a blog post. “Add to that the twist of predicting real-time traffic, pooling multiple riders and making the system economically attractive for everyone — and now you have one of the most challenging computer science problems I’ve encountered in my thirty-year career.”

Singhal will report directly to Kalanick in his role, which oversees Uber’s core functions of mapping and marketplaces.

“I love Amit’s excitement for solving complex computer science problems and his passion for helping improve people’s lives through technology,” Kalanick said in a statement. “The team at Uber, myself included, will learn a lot from him, and I can’t wait for him to get started.”